Separation of gamma benzene hexachloride



Patented May 22, 1951 SEPARATION OF GAMMA BEN ZENE' HEXACHLORIDE Leslie James 'Burrage; Hunts Cross, and James Crosby Smart, Widnes, England, assignors to- Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application. January'27, 1948, Se-

rialN'o; 4;708; InGreat Britain June 11', 1943 6 Claims;

This invention relates to'improvements in the production of organic compounds, and more particularly to the isolationof an isomeric form of benzene hexachloride.-

This application is a continuation-in-part of our copendingapplication Serial Number 537,372, filed'May 25, 1944; now abandoned.

It is known that-benzene hexachloride can beobtained by reacting chlorine with benzene under conditions promoting-- theaddition of chlorine, but not the substitutionof'chlorine for hydro-- gen. The product" so 1 obtained is a mixture of stereoisomers of benzene hexachloride and will be referred to hereinafter astheadditive chlorination product of benzene. The additive chlorination product of benzene is suitably prepared by passing chlorine into benzene in the presence of actinic radiationat temperatures of, say, 50 C. to 60 C. A number of stereoisomers of benzene hexachloridearepossible in the additive chlorination product of benzene, some of which have been described in the literature-, and under the above conditions the alpha isomer, M. P. 158 C. predominates in the product, the beta'isomer, M. P. 305 C., and the-gamma isomer, M. P. 113 0., also being formed.

Hitherto the gamma isomer has been obtained by continuing the chlorinationof the benzene:

until a slurry ofalphab'enzene hexachloridedssubstituted benzene. hexachloride, for. example,- monochlorobenzene hexachloride, which may be formed. On fractional crystallisation some of the alpha isomer; crystallises withv the gamma isomer, makingthe isolation of the latter diflicult andthe method troublesome to carry out;

I The above-identified application, of whichthe present applicationis a continuation-in-part,

discloses that the gamma isomer of benzene hexachloride can be recovered from the product obtainedby the additive chlorination of benzene by removing unchanged benzene and extracting the remaining material in the cold with a lower aliphatic alcohol Theprocess is described with particular reference to methanol.

We have found that the alpha isomer. has but a small solubility. inrthe lower aliphatic alcohols as comparedwith the gamma isomenand' inadvdition thisasolubility appears.;-to be depressed by: the presence.of- .the' gamma isomer, sothat very:

little of theal-pha isomer dissolves unl'es's more than enough solvent used to dissolve allof" the gamma; Thus'a'sepa'ration of the gamma isomer from the-alpha canbe achieved, It is,

however, preferable: in practice to use rathermore than 1 this -mi-nimum quantity of solvents since a part of the-gamma isomer is 'liable to be retained with the :undissolved alphaisomer; and

tion of the solvent followed'by-cooling underquiescent conditions. The beta isomer orother bodies present in the additivev chlorination product: will also be 'presentin the extract. contain-s ing the gamma isomer, but-on crystallisation of the solution as above-the gamma-isomer is deposited first, andcan-thus be recoveredsepae rately. On the other hand, if the presence of these other bodies-is not objectionable,-the whole ofthe solids-may be recovered'from solution together.

According tothe present invention, therefore;

a process for treating the additive chlorination product of benzene to obtain therefrom a benzene hexachloridethaving an enhanced'proportion of the gammaisomer comprises extracting. the said chlorinationproduct with a lower aliphatic alcohol in such-amount as to dissolve; gamma isomer and leave a substantial propor-- tion of; the alpha-isomer undissolved, the weightof the'said alcohol notbei-ng less thanhalf the weight-of the solid :to' be; extracted. The aloe-,- hols methanol and etha-nol are bothparticularly:

suitable for the process of:the- -.in,vention. Where the additive chlorination productof benzene is obtained as a mixture with unchanged-benzene the latter is removed-by'extraction, preferably; by flashing off:by contacting the mixture with,"

hot water: r The minimum quantityaof solvent necessary. to

carry out the :invention will :bethat which gives a mixture of solution and'undissolved material from which it is.- practicable "to separate the formenand this'corresp'onds to approximatelyequal bulks-of solventand crude benzene hexa chloride; Sincethe respective densities'of moth-1' anol and ethanol. are about half that of: benzenehexachloride, on. this: basisithe weight ofsolvent used would-ithusbe equaltoiabout'half the weigh-ti of rthe' solid: taken. This" quantity; of solvent, :1

however, is: not :.a sunicient tomzdissolve all the;

gamma isomer present in the ordinary additive chlorination product of benzene, and the most advantageous amount of solvent will in general be the minimum which will dissolve all the gamma isomer. 7 The latter figure can be approximately calculated by use of the following table showing the relative solubilities of the individual alpha and gamma isomers in methanol and ethanol, given as the number of parts of these isomers present in 100 parts by weight of a saturated solution at 20 C. containing only the one isomer.

Solubility Solvent Alpha Gamma Methyl alcohol 2.06 6.77 Ethyl alcohol 1.77 6.39

Crude benzene hexachloride as obtained by the additive chlorination of benzene in presence of actinic light contains about 12% of the gamma isomer, and the least quantity of solvent required to extract all the gamma isomer would therefore be between one and a half and two times the weight of the total solid. In the case of a benzene hexachloride which contains less than 12% gamma, the theoretical amount of solvent required to dissolve all the gamma would also decrease in accordance with the above formula but should not be less than half the weight of solid taken. Subject to the above limitation, however, the proportion of solvent to solid is not extremely critical.

When only suflicient solvent to dissolve all the gamma isomer is used, comparatively little of the alpha isomer goes into solution. If the presence of small amounts of the alpha isomer is not objectionable, however, rather more of the alcohol may be used, and a corresponding proportion of the alpha isomer will then be present in the extract together with the gamma isomer. In practice, the quantity of solvent required is preferably from one to three times the weight of the material to be extracted.

The extraction may conveniently be carried out in the cold, that is to say at temperatures not greatly different from atmospheric, say from 15 C. to 30 C. The recovery of the product from the extract may then be carried out by fractional crystallisation. For instance, the solution may be heated to evaporate part of the alcohol and the concentrated solution allowed to cool to room temperature. Cooling to below atmospheric temperature, for example to -30 C. or -40 C., may be employed to cause crystallisation to occur instead of or in addition to evaporating off the alcohol; and by successive operations of evaporating alcohol and cooling, several fractions can be obtained. Alternatively, if pure gamma isomer is not required the whole of the solids in the extract may be recovered together by evaporating grams off the alcohol, or by adding water to the extract so that they are precipitated.

When the alcohol is used in amounts such that practically no alpha isomer dissolves, fractional crystallisation will then yield fractions of substantially pure gamma isomer. If the extract contains some alpha isomer, as when the solvent is used in more than minimum quantity, the pure gamma may be obtained by evaporating about two-thirds of the solvent and allowing the remainder of the solution to crystallise while keeping it quiescent. Under these circumstances, although the residue of the solution is supersaturated with the less-soluble alpha isomer the first fraction crystallising out consists of the pure gamma isomer. On the other hand, if after evaporating off part of the solvent the residue is subjected to agitation during cooling, the mixed isomers crystallise in the normal way.

Using methyl or ethyl alcohol, an amount up to an equal weight of the additive chlorination product from which unchanged benzene has been removed can be used to perform the extraction without dissolving any substantial amount of the alpha isomer, and approximately 70% of the alcohol can then be removed from the extract without causing the precipitation on standing of substantial amounts of material other than the gamma isomer. Solvent equal to from one to three times the weight of the additive chlorination product is preferably used to perform the extraction, and a small amount of the alpha isomer then also goes into solution. Removal of about two-thirds of the solvent gives an extract which may be treated in several ways according to the product required. For example, the pure gamma isomer may be obtained by crystallisation under quiescent conditions, the extract may be subjected to normal fractional crystallisation either with agitation or without any special precautions to prevent disturbance of the solution, or the whole of the solvent may be removed to give a gamma concentrate.

The production of the additive chlorination product may be carried out in known manner. For example, chlorine may be passed into benzene at ordinary or elevated temperature while irradiating the benzene with the radiation from a mercury arc lamp, sunlight or other actinic radiation. The introduction of chlorine may be continued until a slurry of benzene hexachloride results, but preferably it is discontinued while all the product is still in solution, since there is then less tendency for chloro-substitution products to form. Conveniently, chlorination is continued until a 15% to 20% solution is obtained.

In one form of the invention benzene is chlorinated while irradiating it with sunlight or the light from a mercury arc lamp by passing in chlorine at such a rate that it is substantially completely absorbed. Suitably the temperature is maintained between 40 C. and 50 C. When the solution formed contains 15% to 20% benzene hexachloride chlorination is stopped, and the solution is added gradually to a large agitated volume of water maintained at C. to C. so that benzene is flashed oil and the benzene hexachloride precipitated; the benzene vapour may be condensed, separated from the water which will be condensed with it, and used for further chlorinations. The precipitated benzene hexachloride is filtered 01f from the water, dried at 30 C. to 35 0., ground, and then treated with between 1 and 3 times its weight 'ofcold methanol with agitation for some time, for; example 2-4 hours, and the resultant solution filtered oil. After extraction, the filter. cake may be washed with additional small, portions of. solvent, and the extract, or combined extract and washings, is then heated so as to evaporate 40% to 70% oi; the methanol and-allowed to cool, care being taken to avoid agitation of the solution. Crystalline gamma benzene hexachloride is thereby deposited and can be separated by filtration or decantation and dried. Alternatively the whole of the solids in solution may be recovered by pouring the solution into at least three times its volume of Water, so that the solids are precipitated; they may then be separated from the liquid by filtration or decantation and dried.

Instead of removing the benzene from the chlorinated material by contacting it with hot water, the benzene may be evaporated off in an externally heated vessel maintained, if desired, under reduced pressure. However, the removal of benzene by means of hot water is a particularly suitable method since efficient removal of the benzene results Without submitting the benzene hexachloride to conditions under which partial decomposition to trichlorobenzene could occur, and since the product is obtained in convenient form for handling.

The gamma benzene hexachloride obtained by the methods of this invention may be used in the manufacture of pest control compositions as described in and claimed in one form of the invention of British Patent specification No. 573,689. The alpha benzene hexachloride may, if desired, be used for other purposes, for example the manufacture of trichlorobenzene.

The following examples illustrate but do not limit our invention, all parts being by weight:

Example 1 Chlorine was passed at the rate of 22 parts per hour into benzene maintained at 50 C. and irradiated with a mercury arc lamp. Absorption of chlorine was substantially complete. After 1 hour chlorination was stopped. The resultant solution of benzene hexachloride was gradually added to a large volume of water maintained at 76 C. to 78 C. and the precipitated product was filtered off, dried in a tray drier for 24 hours, and ground.

1000 parts of the ground benzene hexachloride thus obtained were agitated with 2000- parts of methanol in the cold, and the resultant solution was filtered 01f, heated to evaporate 1220 parts of methanol and then allowed to cool to 16 C. and stand overnight. The crystals which separated were filtered off and dried. 46 parts of the gamma isomer of benzene hexachloride were thus obtained, melting at 110-l13 C.

Example 2 370 parts of crude benzene hexachloride prepared as in Example 1 were stirred at C. for 2 hours with 810 parts of industrial alcohol (containing about 95% ethanol and the remainder methanol and other impurities) and the slurry so obtained was filtered under reduced pressure. The filtrate was heated until all the solvent had evaporated. The residue, consisting of 115 parts of solid material, contained 32% of the gamma isomer. The original crude material contained approximately 12% of the gamma isomer.

Example 3 1000 parts of ground benzene hexachloride prepared, as; inv Example 1 werev agitatediwith- 2400: parts of industrial alcohol at 20 C-.- for 2 hours. The solution so obtainedwas filtered under reduced pressureand the filter. cakewas pressed to remove as much liquid as possible, and then washed twice with 50 parts oiindustrial alcohol. The filtratewas heated to distil off 1700 partsof alcohol. The residual extract was allowed to cool to room temperature and to remain quiescent for-two. days. isomer which formed were-filtered ofi, rinsed quickly with a little alcohol and dried .at about 50 C. 66 parts of pure gamma isomer were obtained.

We claim:

1. A process for treating the total additive chlorination product of benzene to obtain therefrom a benzene hexachloride product having an enhanced proportion of gamma isomer Which comprises extracting said isomer mixture with a cold lower saturated aliphatic monohydric alcohol having not over 2 carbon atoms in such amount as to dissolve only a part of said mixture and leave a substantial portion of said mixture undissolved, the weight of said alcohol being not less than half the weight of said isomer mixture.

2. A process for treating the total additive chlorination product of benzene to obtain therefrom a benzene hexachloride product having an enhanced proportion of gamma isomer which comprises extracting said isomer mixture with cold methanol in such amount as to dissolve only a part of said mixture and leave a substantial portion; of said mixture undissolved, the weight of said alcohol being not less than half the Weight of said isomer mixture.

3. A process for treating the total additive chlorination product of benzene to obtain therefrom a benzene hexachloride product having an enhanced proportion of gamma isomer which comprises agitating said isomer mixture in the cold with a lower saturated aliphatic monohydric alcohol having not over 2 carbon atoms in such amount as to dissolve only a part of said mixture and leave a substantial portion of said mixture undissolved, the weight of said alcohol being not less than half the weight of said isomer mixture, separating the resulting solution from the undissolved portion of said isomer mixture, causing the said solution to deposit crystals while maintaining it quiescent and separating the precipitated crystals of gamma benzene hexachloride from the supernatant liquor.

4. A process as claimed in claim 3, wherein said alcohol is methanol.

5. A process as claimed in claim 3, wherein said solution is caused to deposit crystals by heating the solution to evaporate off part of the alcohol therefrom and then cooling the concentrated solution.

6. A process for the production of gamma benzene hexachloride which comprises chlorinating benzene under such conditions that additive chlorination occurs and a solution of benzene hexachloride in unchanged benzene is obtained, evaporating unchanged benzene from said solution to yield a solid mixture of benzene hexachloride isomers containing all the isomers formed in said additive chlorination, extracting said solid mixture in the cold with a lower saturated aliphatic monohydric alcohol having not more than two carbon atoms in such amount as to dissolve only a part of said mixture and leave a substantial portion of said mixture undissolved,

the weight of said alcohol being not less than Crystals of gamma half the weight of said isomer mixture, heating the resulting solution to evaporate ofi a part of the alcohol content thereof, cooling the concentrated extract and separating the resulting precipitated gamma benzene hexachloride from the supernatant liquor.

LESLIE JAMES BURRAGE.

JAMES CROSBY SMART.

REFERENCES CITED The following references are of record in the file of this patent:

8 FOREIGN PATENTS Number Country Date 447,058 Great Britain May 7, 1936 573,693 Great Britain Dec. 3, 1945 OTHER REFERENCES 10 ed., pages 724-5 (1942). 

1. A PROCESS FOR TREATING THE TOTAL ADDITIVE CHLORINATION PRODUCT OF BENZENE TO OBTAIN THEREFROM A BENZENE HEXACHLORIDE PRODUCT HAVING AN ENHANCED PROPORTION OF GAMMA ISOMER WHICH COMPRISES EXTRACTING SAID ISOMER MIXTURE WITH A COLD LOWER SATURATED ALIPHATIC MONOHYDRIC ALCOHOL HAVING NOT OVER 2 CARBON ATOMS IN SUCH AMOUNT AS TO DISSOLVE ONLY 2 PART OF SAID MIXTURE AND LEAVE A SUBSTANTIAL PORTION OF SAID MIXTURE UNDISSOLVED, THE WEIGHT OF SAID ALCOHOL BEING NOT LESS THAN HALF THE WEIGTH OF SAID ISOMER MIXTURE. 